Crackle finish coating of arylene sulfide polymer containing a fluorocarbon polymer

ABSTRACT

A decorative crackle arylene sulfide polymer coating is provided by first subjecting the arylene sulfide polymer and a light colored pigment such as titanium dioxide to intensive milling and thereafter mixing the resulting blend with a fluorocarbon polymer in the presence of water and a dispersing agent utilizing a less intensive mixing technique such as a propeller driven blender.

United States Patent [191 Tieszen Dec. 23, 1975 1 CRACKLE FINISH COATINGOF ARYLENE SULFIDE POLYMER CONTAINING A FLUOROCARBON POLYMER [75]Inventor: Dale 0. Tieszen, Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

[22] Filed: Sept. 13, 1974 [21] Appl. No.: 505,919

Related US. Application Data [62] Division of Ser. No. 299,066, Oct. 19,1972, Pat. No.

[52] US. Cl. 427/257; 427/385; 427/388 [51] Int. Cl. B05D 5/00 [58]Field of Search 117/38, 41, 119.6, 161UG, 117/132 B, 132, CF, 132 A;260/291, 37 P, 29.6 F, 33.4 F, 900

[56] References Cited UNITED STATES PATENTS 3,622,376 11/1971 Tieszen eta1. 117/132 B Primary ExaminerThomas J. Herbert, Jr. AssistantExaminerBruce H. Hess [57] ABSTRACT 10 Claims, No Drawings BACKGROUND ETHE INVENTION This invention relates to the preparation of cracklefinish arylene sulfide polymer coatings.

Arylene sulfide polymers are known for their desirableflcharacteristicsas coating compositions as shown by Ray US. Pat. No.-3,492,l25.'Becauseof the hard-' ness and durability of such coatings they are of value formany applications including decorative coatings on appliances,housewares, and the like. It has been found desirable in some instancesto incorporate a fluorocarbon polymer with the arylene sulfide polymer.While such compositions can tend' to give rough coatings, certainprecise techniques have been developedfor circumventing this problem andobtaining the same smooth'coating of uniform appearance with a fluoro-..carbon present as is obtained without the fluorocarbon.

. BRIEF SUMMARY or THE INvEN'rIoN It is an object of :this invention toprovide an arylene sulfide polymer coating which is not rough but whichnonetheless has a crackle finish.

' It is a further object of this invention to provide a method forincorporating fluorocarbon polymers in arylene sulfide'coatingcomposition so as to achieve a crackle finish.

It is yet a further object of this invention to provide an arylenesulfide polymer coating having a decorative and attractive cracklefinish.

In accordance with this invention, an arylene sulfide polymer inparticulate form is subjected to intensive milling with a light coloredpigment such as titanium dioxide and thereafter mixed under lessintensive conditions with a fluorocarbon polymer in the presence of aliquid capable of wetting the mixture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The instant invention isapplicable to the production of crackle finishes of arylene sulfidepolymer having any normally solid fiuorocarbon polymer incorporatedtherein. It is of particular utility in compositions having highmolecular weightfl'uorocarbon polymer, that is fluorocarbon polymerstofsuch molecular weight that no flow is obtained in the ASTM D 1238 meltviscosity test at 380C using a 5,000 g weight. Such polymers probablyhave a' number average molecular weight greater than 10,000,000. Theseare the types of polymers generally referred to as extrusion or moldinggrade polymers. Such polymers are sold under trademarks Teflon-S',Teflon-6', Teflon-7, and Halon G-80. These polymers pass the FDAspecification for acceptable polytetrafluoroethylene in food servicewhich requires a melt viscosity of at least 10,000 poise at 380C' asdetermined by ASTMD 1238-ai1d a thermal instability index (T11) of lessthan 50 as determined by ASTM D1457. V

Most preferably the fluorocarbon polymer is a mixture of theabove-described high molecular weight polytetrafluoroethylene with alower molecular weight coating grade polytetrafluoroethylene such asthat sold by LNP Corp. as TL-l26. The ratio of high molecular weight tolower molecular weight polytetrafluoroethylene can vary greatly butgenerally will be in the range of l-10 parts by weight of high molecularweight polytetrafluoroethylene to each one part by weight of lowermolecular weight polytetrafluoroethylene.

The invention is applicable to the production of dispersions of anyarylene sulfide polymer although the use of a conventional ball mill, aconventional rod mill,

or a vibratory ball mill. The balls or rods can be made of steel,ceramic materials such asBurundum, and the like. The milling can be doneeither wet or dry although dry milling is preferred.

It is essential that the resultingpigment-arylene sulfide polymermixture thereafter be blended with the fluorocarbon polymer in thepresence of a liquid capable of wetting same such as water containing asurface activeagent under less intensive conditions than those used'forthe initial milling. This blending can be done utilizing a Waringblender or any similar blade type mixing device. lt can also be done bytumbling or shaking the components together. It is essential that thematerial at this point not be subjected to intensive milling such asobtained in a ball mill because the fluorocarbon polymer willagglomerate and give a rough finish. Thus, the first step utilizes amilling operation as that word is conventionally used in the art todesignate intensive milling procedures such as ball milling and thesecond step utilizes a blending operation as that word is conventionallyused in the art to designate less intensive simple mixing operationssuch as blending with a propeller.

Any light colored pigment capable of withstanding a curing temperatureof at least about 300F, preferably 600-800F can be utilized. Thepreferred pigment is titanium dioxide or compositions comprising a majoramount of titanium dioxide and a minor amount of another pigment.

The liquid in which the mixture is ultimately blended can be any liquidcapable of wetting the mixture. The preferred liquid is water containinga surface active agent. Other suitable liquids include ethylene glycol,propylene glycol, and mixtures of such liquids with water. Anyconventional surface active agent can be utilized, however, nonionicsurface active agents are preferred.

The ratio of solids (comprising the arylene sulfide polymer, pigment,and fluorocarbon polymer) to liquid can vary depending on a particularcoating application; however, it is generally preferred to have adispersion with about 15 to 60, preferably 25 to 50 weight percentsolids.

The intensive milling times can vary depending on the type of mixtureutilized, with the conventional ball mill or rod mill dry mixing timesgenerally being 5-100, preferably 10-48 hours. With a high speedvibrator with stainless steel balls such .as a Vibratom mill the sameintensive milling can be accomplished in $42 hour to 5 hours or so.

The subsequent blending under less intensive conditions generallyrequires only a matter of minutes, usually l-60, preferably 5-15minutes. Of Course, this again can vary considerably depending on thetype of blending apparatus utilized.

The ratio of arylene sulfide polymer to fluorocarbon in the final curedcoating composition will generally range from 3:1 to 30:1, preferably5:1 to 20:1 based on weight.

The ratio of arylene sulfide polymer to pigment will generally be in therange of 1:1 to :1 based on weight.

It is essential that the pigment, fluorocarbon polymer, and arylenesulfide polymer be in a particulate form. In general, the smaller theparticle size the better the dispersions which can be produced. Asuitable particle size for the fluorocarbon polymer is 40 mesh orsmaller. The pigment can be the same particle size (40 mesh) or smaller.The arylene sulfide polymer will generally be about 40 mesh or smalleralthough satisfactory results can be obtained with coarser material, forinstance 30 mesh or smaller. The intensive milling will generally reducethe arylene sulfide polymer particle size with the final particle sizegenerally being below 100 mesh (Standard U.S. Sieve Series).

The final dispersion can be applied to a substrate by any conventionalmeans such as spraying, or with a doctor blade or the like. Theresulting coating can be cured, for instance, by heating to atemperature of at least 500F, preferably 600-850F for at least 5minutes, preferably minutes to 2 hours. Alternatively, the coatings canbe cured at higher temperatures for shorter times. Coating thicknessescan vary depending on the particular application but generally will be afraction of a mil thicker than smooth coatings not having a cracklefinish. A thickness of 1-3 mils is desirable in most instances.

The resulting coatings while not of primary utility for nonstick foodapplications nonetheless are relatively smooth in spite of the crackleappearance.

EXAMPLE A dispersion of polyphenylene sulfide having an inherentviscosity of about 0.15, as determined using 0.25 percent of the sampleand chloronaphthalene at 206C, and a particle size of less than 60 mesh,were made by mixing 150 g of said polyphenylene sulfide with 50 g oftitanium dioxide in a laboratory rod mill for 16 hours. Thereafter 80 gof this mix, 4.5 g of a high molecular weight polytetrafluoroethylenesold by Du- Pont under the trademark Teflon-7, and 1.5 g of a lowermolecular weight polytetrafluoroethylene sold by LNP Corp. as TL-126were blended with 120 g of water containing one percent of a nonionicsurface active agent (octylphenoxypolyethoxy ethanol) sold under thetrademark Triton X-l00 by Rohm & Haas Co. were blended in a Waring mixerfor 10 minutes. The resulting dispersion was sprayed with a Binks Model188 spray gun onto 3 X 6 X 0.020 inch aluminum alloy coupons which hadbeen degreased by washing in acetone and blasted with a No. 100abrasive. The resulting coatings were cured at 700F for 30 minutes. Thecoating thickness was two mils. The resulting coating was relativelysmooth to the touch but had a crackle appearance.

CONTROL l A dispersion identical to that of the Example was made in anidentical manner except red iron oxide was used in place of titaniumdioxide. The resulting coating had a smooth appearance with noindication of a crackle finish.

CONTROL Il Ninety grams of polyphenylene sulfide identical to thatutilized in the Example, 30 g of titanium dioxide identical to that ofthe Example, 6.75 g of high molecular weight polytetrafluoroethyleneidentical to that of the Example, 2.25 g of low molecular weightpolytetrafluoroethylene identical to that of the Example, and 250 g ofwater containing 3 g of a surface active agent identical to that of theExample were ball milled together for 16 hours and sprayed ontoidentical coupons in an identical manner to that of the Example. Theresulting coating was rough, being useless as a release coating andhaving an unattractive appearance.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

1 claim:

1. A process for forming a coated article comprising:

applying to a substrate a dispersion formed by subjecting a poly(arylenesulfide) in particulate form to intensive milling by ball milling or rodmilling with a light colored pigment in particulate form capable ofwithstanding a curing temperature of at least about 300 F; thereafterunder less intensive conditions blending the resulting mixture by blademixing, tumbling, or shaking with a fluorocarbon polymer in particulateform, in the presence of a liquid selected from the group consisting ofwater, ethylene glycol, propylene glycol, and mixtures thereof; and

heating said thus applied dispersion at a temperature of at least 500Ffor at least 5 minutes to obtain a cured coating having a cracklefinish.

2. method according to claim 1 wherein said fluorocarbon polymer ispolytetrafluoroethylene and said pigment is titanium dioxide. I

3. A method according to claim 2 wherein a ratio of said poly( arylenesulfide) to said fluorocarbon polymer in said cured coating is withinthe range of 3:1 to 30:1 based on weight.

4. A method according to claim 3 wherein said liquid is water containinga surface active agent.

5. A method according to claim 4 wherein said poly- (arylene sulfide) ispolyphenylene sulfide.

6. A method according to claim 5 wherein said poly- (arylene sulfide)has a particle size of 40 mesh or smaller, said fluorocarbon polymer hasa particle size of 40 mesh or smaller, and said pigment has a particlesize of 40 mesh or smaller.

7. A method according to claim 5 wherein the ratio of said arylenesulfide polymer to pigment is within the range of 1:1 to 10:1 based onweight and the total solids content in said dispersion is within therange of 15 to 60 percent based on the total weight of said dispersion.

8. A method according to claim 1 wherein said dispersion is applied tosaid substrate by means of spraymg.

9. A method according to claim 1 wherein said dispersion is heated to atemperature of 600 to 850F for 15 minutes to 2 hours to effect saidcure.

10. A coated article produced by the method of claim 1.

1. A PROCESS FOR FORMING A COATED ARTICLE COMPRISING: APPLYING TO ASUBSTRATE A DISPERSION FORMED BY SUBJECTING A POLY(ARYLENE SULFIDE) INPARTICULATE FORM TO INTENSIVE MILLING BY BALL MILLING OR ROD MILLINGWITH A LIGHT COLORED PIGMENT IN PARTICULATE FORM CAPABLE OF WITHSTANDINGA CURING TEMPERATURE OF AT LEAST ABOUT 300* F., THEREAFTER UNDER LESSINTENSIVE CONDITIONS BLENDING THE RESULTING MIXTURE BY BLADE MIXING,TUMBLING, OR SHAKING WITH A FLUOROCARBON POLYMER IN PARTICULATE FORM, INTHE PRESENCE OF A LIQUID SELECTED FROM THE GROUP CONSISTING OF WATER,ETHYLENE GLYCOL, PROPYLENE GLYCOL, AND MIXTURES THEREOF; AND HEATINGSAID THUS APPLIED DISPERSION AT A TEMPERATURE OF AT LEAST 500* FOR ATLEAST 5 MINUTES TO OBTAIN A CURED COATING HAVING A CRACKLE FINISH.
 2. Amethod according to claim 1 wherein said fluorocarbon polymer ispolytetrafluoroethylene and said pigment is titanium dioxide.
 3. Amethod according to claim 2 wherein a ratio of said poly(arylenesulfide) to said fluorocarbon polymer in said cured coating is withinthe range of 3:1 to 30:1 based on weight.
 4. A method according to claim3 wherein said liquid is water containing a surface active agent.
 5. Amethod according to claim 4 wherein said poly(arylene sulfide) ispolyphenylene sulfide.
 6. A method according to claim 5 wherein saidpoly(arylene sulfide) has a particle size of 40 mesh or smaller, saidfluorocarbon polymer has a particle size of 40 mesh or smaller, and saidpigment has a particle size of 40 mesh or smaller.
 7. A method accordingto claim 5 wherein the ratio of said arylene sulfide polymer to pigmentis within the range of 1:1 to 10:1 based on weight and the total solidscontent in said dispersion is within the range of 15 to 60 percent basedon the total weight of said dispersion.
 8. A method according to claim 1wherein said dispersion is applied to said substrate by means ofspraying.
 9. A method according to claim 1 wherein said dispersion isheated to a temperature of 600* to 850*F for 15 minutes to 2 hours toeffect said cure.
 10. A coated article produced by the method of claim1.